Subacute sclerosing panencephalitis always fatal

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Note that this study was published as an abstract and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.

A rare and universally fatal complication of measles, subacute sclerosing panencephalitis (SSPE), is more common than clinicians had thought.

Note that the report comes as the World Health Organization has declared the Americas to be free of measles, although unvaccinated travelers can still bring cases into the country and -- if they have contact with other unvaccinated people -- can cause an outbreak.

NEW ORLEANS -- A rare and universally fatal complication of measles is more common than clinicians had thought, a researcher said here.

The disease is subacute sclerosing panencephalitis (SSPE) and in the pre-vaccine era investigators thought it occurred about one in 100,000 measles cases, according to James Cherry, MD, of the University of California Los Angeles.

SSPE is a long-term outcome of measles, typically appearing 4 to 8 years after measles infection, and characterized initially by behavior changes and later by progressively more severe seizures. Death usually occurs between 1 and 3 years after diagnosis.

The definitive diagnosis comes at autopsy, when measles antibodies can be found in the cerebrospinal fluid and measles antigens or inclusion bodies in brain tissue, Cherry said.

"We used to think it was quite rare," Cherry said, but a study from German researchers in 2013 suggested the rate was about one in 1,700 measles infections among children under age five. The "really striking" findings of the current study suggest that is still an underestimate, he said.

Importantly, many patients could be shown to have been vaccinated on time, but to have had measles in the first year of life, before the live attenuated vaccine can be given, Cherry and colleagues found.

"We need to be thinking about herd immunity," he said, because what protects infants is making sure that everyone around them is immune to the disease.

The report comes as the World Health Organization has declared the Americas to be free of measles, noted Gary Marshall, MD, of the University of Louisville School of Medicine, who was not involved in the study but who moderated a media briefing at which it was discussed.

"That doesn't mean there is no measles," he said.

Instead, he said, it means that unvaccinated travelers can still bring cases into the country and -- if they have contact with other unvaccinated people -- can cause an outbreak, although there is no widespread sustained transmission.

Indeed, so far this year, 54 cases have been reported in the U.S., according to the CDC. The recent record is held by 2014, a year in which 667 cases were reported, the largest total since 2000.

The researchers found 11 cases in the project files -- seven by looking at death certificates, and one from a report by the CDC.

All of the patients except one have died. The exception, a 3-year-old boy, was infected as an infant during travel outside the U.S., recently developed SSPE, and is in hospice care, the researchers reported.

The 17 cases occurred from 1998 through 2015, about half of the patients were U.S.-born, and three-quarters belonged to ethnic minorities. Twelve patients had confirmed measles or a compatible febrile illness with rash when they were younger than 15 months, with 11 younger than a year.

The researchers were able to use data from the 1988-1990 outbreak to calculate estimated rates of SSPE:

Some 9,564 children younger than age five had measles in the outbreak, including seven SSPE cases exposed at the time. The numbers yield a risk ratio of 1 to 1,367.

And 3,651 children were less than one when they caught measles during the outbreak, including six who later developed SSPE, yielding a risk ratio of 1 to 609.

The researchers cautioned that the analysis is retrospective and the conclusions might vary if some of the underlying numbers are incorrect. For instance, if the number of measles cases were higher than was reported, that would tend to lower the risk of SSPE. Conversely, if the actual number of SSPE cases was higher, that would increase the risk.

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